scholarly journals Two Astrometric Projects: LIGHT (Light Interferometer Satellite for the studies of Galactic Halo Tracers) and MIRA (Mitaka/Mauna Kea/Maui Optical and Infra-Red Interferometer Array)

1997 ◽  
Vol 165 ◽  
pp. 561-566
Author(s):  
M. Yoshizawa ◽  
K. Sato ◽  
J. Nishikawa ◽  
T. Fukushima ◽  
M. Miyamoto
Keyword(s):  
Galactic Halo ◽  
Basic Structure ◽  
Proper Motions ◽  
Infra Red ◽  
The Galaxy ◽  
Galactic Astronomy ◽  
Fringe Patterns ◽  
Almost All ◽  
Ccd Arrays ◽  
Better Than

AbstractThe projects LIGHT and MIRA are the space-borne and ground-based optical/Infrared-interferometer projects of the National Astronomical Observatory of Japan. The contents of each project are gradually developing, and the descriptions given below are the preliminary ones studied at the present time.LIGHT (Light Interferometer satellite for the studies of Galactic Halo Tracers) is a scanning astrometric satellite for stellar and galactic astronomy planned to be launched between 2007 and 2010 by a M-V launcher of ISAS, Japan. Two sets of Fizeau-type 40cm-pupil interferometers with 1 m baseline are the basic structure of the satellite optics. The multi-color (U, B, V, R, I, and K) CCD arrays are planned to be used in the focal plane of the interferometer, optimized for detecting the precise locations of fringe patterns. LIGHT is expected to observe the parallaxes and proper motions of nearly a hundred million stars up to 18th visual (15thK-band) magnitude with the precision better than 0.1 milli-arcsecond (about 50 microarcsecond in V-band and 90 micro-arcsecond in K-band) in parallaxes and better than 0.1 milli-arcsecond per year in proper motions, as well as the precise photometric characteristics of the observed stars. Almost all of the giant and supergiant stars belonging to the disk and halo components of our Galaxy within 10 to 15 kpc from the sun will be observed by LIGHT to study the most fundamental structure and evolution of the Galaxy. LIGHT will become a precursor of a more sophisticated future astrometric interferometer satellite like GAIA (Lindegren and Perryman, 1996).

scholarly journals A Complete, Multicolour Survey of Absolute Proper Motions in the Anticentre Direction at Intermediate Latitude: Kinematics of the Galaxy's Stellar Populations

1994 ◽  
Vol 161 ◽  
pp. 447-449
Author(s):  
D.K. Ojha ◽  
O. Bienaymé ◽  
A.C. Robin
Keyword(s):  
Stellar Populations ◽  
Proper Motions ◽  
The Galaxy ◽  
Ubv Photometry ◽  
Better Than

We present the observational results of UBV photometry and absolute proper motions in the anticentre direction at intermediate latitude (l = 167.5°, b = 47.4°) for an 8.6 square degree field. The sample is complete down to V = 17, and the accuracy of the proper motions is better than per century for stars brighter than V = 16. It is attempted here to make an investigation of the structure and kinematics of the Galaxy from absolute proper motions. Details of the present work can be found elsewhere (Ojha et al. 1993).

scholarly journals Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S248) ◽  
pp. 141-147 ◽  
Author(s):  
M. J. Reid
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Proper Motions ◽  
Star Forming ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A ◽  
Definition Of ◽  
Almost All

AbstractThe VLBA is now achieving parallaxes and proper motions with accuracies approaching the micro-arcsecond domain. The apparent proper motion of Sgr A*, which reflects the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0/R0 and offers a dynamical definition of the Galactic plane with Sgr A*at its origin. The intrinsic motion of Sgr A*is very small and comparable to that expected for a supermassive black hole. Trigonometric parallaxes and proper motions for a number of massive star forming regions (MSFRs) have now been measured. For almost all cases, kinematic distances exceed the true distances, suggesting that the Galactic parameters, R0 and Θ0, are inaccurate. Solutions for the Solar Motion are in general agreement with those obtained from Hipparcos data, except that MSFRs appear to be rotating slower than the Galaxy. Finally, the VLBA has been used to measure extragalactic proper motions and to map masers in distant AGN accretion disks, which will yield direct estimates of H0.

scholarly journals 9.1. HST detections of massive black holes in the centers of galaxies

1998 ◽  
Vol 184 ◽  
pp. 377-384 ◽  
Author(s):  
H.C. Ford ◽  
Z.I. Tsvetanov ◽  
L. Ferrarese ◽  
W. Jaffe
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Hubble Space Telescope ◽  
Spherical Aberration ◽  
Proper Motions ◽  
Black Hole Mass ◽  
Massive Black Holes ◽  
The Galaxy ◽  
Ngc 1068 ◽  
Better Than

After correcting spherical aberration in the Hubble Space Telescope in 1993, the central masses of galaxies can be measured with a resolution 5 to 10 times better than can be achieved at the best terrestrial sites. This improvement in resolution is decisive for detecting the gravitational signature of massive black holes in galaxy nuclei. The discovery of small (r ~ 100–200 pc) rotating gaseous and stellar disks in the centers of many early-type galaxies provides a new and efficient means for measuring the central potentials of galaxies. Concomitantly, VLBI observations of H2O masers in the nuclei of NGC 4258 and NGC 1068 revealed exquisite Keplerian rotation curves around massive black holes at radii as small as 0.1 pc. Recent terrestrial K-band measurements of the proper motions of stars in the cluster at the center of the galaxy provide irrefutable evidence for a black hole with a mass of 2.7 × 106M⊙. At the time of this symposium, the presence of central massive black holes has been established in 12 galaxies. The evidence suggests that there are massive black holes in the centers of all AGNs and in most, if not all, nucleated galaxies. The present data show at best a weak correlation between black hole mass and bulge luminosity.

scholarly journals Masers and the Cosmic Distance Scale

1988 ◽  
Vol 129 ◽  
pp. 169-174 ◽  
Author(s):  
Mark J. Reid ◽  
James M. Moran ◽  
Carl R. Gwinn
Keyword(s):  
Sufficient Accuracy ◽  
Distance Scale ◽  
Proper Motions ◽  
Fundamental Parameters ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Extragalactic Distance Scale ◽  
Maser Sources ◽  
Better Than

Studies of H2O masers have demonstrated the power of VLBI techniques to measure relative positions with sufficient accuracy (∼ 10 μas) to determine proper motions and to estimate distances to maser sources throughout the Galaxy. The distance to four H2O masers have been determined, and the distance to the center of the Galaxy has been determined to be 7.1 ± 1.5 kpc from observations of the H2O masers in Sgr-B2. Proper motion distances for other H2O masers, and possibly for OH masers, may allow the determination of the fundamental parameters describing the size (Ro) and rotation rate (Θo) of the Galaxy with accuracies of better than 10%. Finally, the measurement of the proper motions of H2O masers in nearby galaxies (< 10 Mpc) is feasible and offers the possibility of direct calibration of the extragalactic distance scale.

scholarly journals Models for the dynamical evolution of the Magellanic System

2008 ◽  
Vol 4 (S256) ◽  
pp. 105-116
Author(s):  
Kenji Bekki
Keyword(s):  
Galactic Halo ◽  
Dynamical Evolution ◽  
Magellanic Clouds ◽  
Young Stars ◽  
Proper Motions ◽  
Self Consistent ◽  
The Galaxy ◽  
Formation And Evolution ◽  
Magellanic Stream ◽  
Magellanic System

AbstractI discuss the following five selected topics on formation and evolution of the LMC and the SMC based on fully self-consistent chemodynamical simulations of the Magellanic Clouds (MCs): (1) formation of bifurcated gaseous structures and young stars in the Magellanic bridge (MB), (2) formation of the Magellanic stream (MS) due to the tidal interaction between the LMC, the SMC, and the Galaxy within the last 2 Gyrs, (3) origin of the observed kinematical differences between H i gas and stars in the SMC, (4) formation of stellar structures dependent on their ages and metallicities in the LMC, and (5) a new common halo model explaining both the latest HST ACS observations on the proper motions of the LMC and the SMC and the presence of the MS in the Galactic halo. I focus exclusively on the latest developments in numerical simulations on formation and evolution of the Magellanic system.

scholarly journals Catalogs of Wide Binaries: Impact on Galactic Astronomy

2006 ◽  
Vol 2 (S240) ◽  
pp. 316-325
Author(s):  
Julio Chanamé
Keyword(s):  
Galactic Disk ◽  
Critical Role ◽  
Proper Motions ◽  
Large Samples ◽  
Large Numbers ◽  
The Galaxy ◽  
Stellar Halo ◽  
Galactic Astronomy ◽  
Early Galaxy

AbstractWide binaries, particularly in large numbers and as free from selection biases as possible, constitute a largely overlooked tool for studying the Galaxy. The goal of this review is to highlight the potential inherent to large samples of field wide binaries for research on problems as varied as star formation in the early Galaxy, the nature of halo dark matter, the evolution of the stellar halo, new geometric distances, metallicities, masses, and ages of field stars and white dwarfs, and much more. Using the Revised NLTT as an illustrative example, I review the main steps in the assembly of a large catalog of wide binaries useful for multiple applications. The capability of cleanly separating between the Galactic disk and halo populations using good colors and proper motions is emphasized. The critical role of large surveys for research on wide binaries as well as for the better understanding of the Galaxy in general is stressed throughout. Finally, I point out the potential for assembling new samples of wide binaries from available proper-motion surveys, and report on current efforts of using the SDSS towards this goal.

Galactic orbits of stars

1966 ◽  
Vol 25 ◽  
pp. 93-97
Author(s):  
Richard Woolley
Keyword(s):  
Globular Cluster ◽  
Potential Field ◽  
High Velocity ◽  
Velocity Vector ◽  
Variable Stars ◽  
The Sun ◽  
Proper Motions ◽  
Rr Lyrae ◽  
The Galaxy

It is now possible to determine proper motions of high-velocity objects in such a way as to obtain with some accuracy the velocity vector relevant to the Sun. If a potential field of the Galaxy is assumed, one can compute an actual orbit. A determination of the velocity of the globular clusterωCentauri has recently been completed at Greenwich, and it is found that the orbit is strongly retrograde in the Galaxy. Similar calculations may be made, though with less certainty, in the case of RR Lyrae variable stars.

scholarly journals 2D kinematics of massive stars near the Galactic Centre

2020 ◽  
Vol 500 (3) ◽  
pp. 3213-3239
Author(s):  
Mattia Libralato ◽  
Daniel J Lennon ◽  
Andrea Bellini ◽  
Roeland van der Marel ◽  
Simon J Clark ◽  
...  
Keyword(s):  
Moving Objects ◽  
Hubble Space Telescope ◽  
Massive Stars ◽  
Line Of Sight ◽  
Galactic Centre ◽  
Harsh Environment ◽  
Proper Motions ◽  
Sgr A ◽  
Better Than ◽  
Rule Out

ABSTRACT The presence of massive stars (MSs) in the region close to the Galactic Centre (GC) poses several questions about their origin. The harsh environment of the GC favours specific formation scenarios, each of which should imprint characteristic kinematic features on the MSs. We present a 2D kinematic analysis of MSs in a GC region surrounding Sgr A* based on high-precision proper motions obtained with the Hubble Space Telescope. Thanks to a careful data reduction, well-measured bright stars in our proper-motion catalogues have errors better than 0.5 mas yr−1. We discuss the absolute motion of the MSs in the field and their motion relative to Sgr A*, the Arches, and the Quintuplet. For the majority of the MSs, we rule out any distance further than 3–4 kpc from Sgr A* using only kinematic arguments. If their membership to the GC is confirmed, most of the isolated MSs are likely not associated with either the Arches or Quintuplet clusters or Sgr A*. Only a few MSs have proper motions, suggesting that they are likely members of the Arches cluster, in agreement with previous spectroscopic results. Line-of-sight radial velocities and distances are required to shed further light on the origin of most of these massive objects. We also present an analysis of other fast-moving objects in the GC region, finding no clear excess of high-velocity escaping stars. We make our astro-photometric catalogues publicly available.

scholarly journals Abundances in the Gaseous Galactic Halo

1998 ◽  
Vol 11 (1) ◽  
pp. 86-89
Author(s):  
Ulysses J. Sofia
Keyword(s):  
Interstellar Medium ◽  
Gas Phase ◽  
High Velocity ◽  
Galactic Halo ◽  
Solar Neighborhood ◽  
Local Interstellar Medium ◽  
The Galaxy ◽  
Metal Abundances ◽  
High Velocity Clouds

Abstract The well measured gas-phase abundances in the low halo suggest that this region of the Galaxy has total (gas plus dust) metal abundances which are close to those in the solar neighborhood. The gas-phase abundances in the halo are generally higher than those seen in the disk, however, this affect is likely due to the destruction of dust in the halo clouds. Observations of high velocity clouds (HVCs) in the halo suggest that these clouds have metal abundances which are substantially lower than those measured for the local interstellar medium. These determinations, however, are often of lower quality than those for the low halo because of uncertainties in the hydrogen abundances along the sightlines, in the incorporation of elements into dust, and in the partial ionization of the clouds.

scholarly journals CPC2 Reduction with Hipparcos and Proper Motions in The Southern Hemisphere

1998 ◽  
Vol 11 (1) ◽  
pp. 551-551
Author(s):  
N. Zacharias ◽  
M.I. Zacharias ◽  
C. de Vegt ◽  
C.A. Murray
Keyword(s):  
Southern Hemisphere ◽  
Systematic Errors ◽  
Reference Star ◽  
Proper Motions ◽  
Positional Accuracy ◽  
Star Catalog ◽  
Naval Observatory ◽  
Celestial Reference System ◽  
First Time ◽  
Better Than

The Second Cape Photographic Catalog (CPC2) contains 276,131 stars covering the entire Southern Hemisphere in a 4-fold overlap pattern. Its mean epoch is 1968, which makes it a key catalog for proper motions. A new reduction of the 5687 plates using on average 40 Hipparcos stars per plate has resulted in a vastly improved catalog with a positional accuracy of about 40 mas (median value) per coordinate, which comes very close to the measuring precision. In particular, for the first time systematic errors depending on magnitude and color can be solved unambiguously and have been removed from the catalog. In combination with the Tycho Catalogue (mean epoch 1991.25) and the upcoming U.S. Naval Observatory CCD Astrograph Catalog (UCAC) project proper motions better than 2 mas/yr can be obtained. This will lead to a vastly improved reference star catalog in the Southern Hemisphere for the final Astrographic Catalogue (AC) reductions, which will then provide propermotions for millions of stars when combined with new epoch data. These data then will allow an uncompromised reduction of the southern Schmidt surveys on the International Celestial Reference System (ICRS).

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